This invention relates to a method and apparatus for removing and treating a gas, particularly a flammable gas, from a low pressure gas source. Still more particularly it relates to such a method and apparatus for removing a gaseous hydrocarbon, such as methane, from a subterranean formation to provide a nonexplosive mixture of the gas and air for disposal.
Gaseous hydrocarbons occur in subterranean formations and may be formed as the result of degradation of heavier hydrocarbons, coal or other organic materials. These hydrocarbon gases can migrate to the earth's surface through porous subterranean formations such as limestone, sandstone, sand or the like. Oftentimes, the combination of the formation pressure, the rate of migration and the quantity of escaping gas is such that commercial recovery of the gas is not feasible. In a low pressure formation not sealed by an impermeable barrier the formation pressure may be slightly higher than atmosphere pressure while still being low enough that the gas does not readily escape to the atmosphere. Nevertheless, a fire or explosive hazard may be present even when there is a low flow rate of gas from a low pressure formation and the escaping gas mixes with air in the atmosphere.
The above problem is of particular concern when it occurs in populated areas, or in the vicinity of other flammable materials, such as airports, petroleum refineries, oil storage facilities or the like. Therefore, it is desirable in such instances to remove the hydrocarbons in a controlled manner for safe disposal to reduce such hazards.
It is well known that certain mixtures of hydrocarbon gases and air are either flammable or explosive, depending upon the concentration of the particular gas in the air. For example, it is known that such a mixture containing above 15 volume percent methane in air will sustain combustion, and that between 5 and 15 percent volume percent methane, the mixture is explosive. Below 5 volume percent methane in air, the mixture is non-flammable and non-explosive.
It is also known to use venturi type devices for removing gases from water wells. Further, it is known to use a venturi arrangement in combination with a mixing chamber and air blower for cleaning discharge gases of particulates and the like. For example, smoke abatement apparatus has been disclosed wherein smoke is aspirated by a wetting fluid in a venturi where it is scrubbed and passed into a tank where emulsified materials from the smoke are collected.
However, such prior art apparatus is not satisfactory for aspirating gas from a low pressure source of gas, for example, methane from a low pressure subterranean formation, and emitting therefrom a non-explosive mixture of the gas in air. Nor is such apparatus self-contained and portable, while being reliable, safe and simple to operate and, further, economic to build and operate.